1. Field of the Invention:
The present invention relates generally to nuclear reactors, and more particularly to a system for transferring nuclear fuel assemblies between a fuel handling building having a spent fuel storage pool or pit disposed therein, and a reactor handling pool defined within the nuclear reactor containment area.
2. Description of the Prior Art:
The fuel for large nuclear reactors, of the type, for example, employed for generating electrical power, is contained within long, small diameter fuel rods or elements which may vary in length from approximately 12-20 feet. Typically, approximately 225-400 fuel elements are arranged in a predetermined pattern within a fuel assembly, spaces being provided or defined between the fuel elements for the reception of vertically adjustable control rods. Although the number of fuel assemblies disposed within reactors will vary depending upon the size of the reactor and the desired power requirements thereof, a perspective of reactor size may be appreciated from the fact that an 1100 megawatt reactor will in fact contain approximately two hundred fuel assemblies.
When the fuel assemblies are properly disposed within the reactor, and the reactor is rendered operative, the nuclear fission process consumes the fuel within an appreciable period of time thereby necessitating the removal of the old fuel assemblies and the replacement of the same with new fuel assemblies containing fresh fuel. Since the metallic rods and other supporting structures comprising each fuel assembly become radioactive, the operation which effects the replacement of the old fuel assemblies with the new fuel assemblies must be accomplished in an entirely underwater mode so as to avoid any hazards due to the radiation. In addition, since the old fuel elements have been heated to a considerable elevated temperature by means of the nuclear fission process, and will continue to produce substantial amounts of heat from the decay process for a period of at least several months, the old fuel assemblies cannot simply be immediately removed from the plant, but to the contrary, must be stored in an underwater environment which therefore provides radiation protection from, and the necessary cooling of, the fuel assemblies. Conventionally, therefore, each old or spent fuel assembly is removed from the reactor core and transported to a spent fuel storage pool or pit. Subsequently, when the old or spent fuel assemblies have decayed sufficiently, they may be removed from the storage pool or pit and shipped out from the plant for suitable disposal, reprocessing, or other viable disposition processing.
Since it will obviously be imperative that the reactor be operative with its freshly replaced fuel assemblies while the spent fuel assemblies are disposed within the storage pool or pit, the spent fuel storage pit must be located externally of the reactor core and container vessel. Since the reactor container vessel is designed to withstand relatively high pressures, and to provide radiation shielding, it is impractical and uneconomical to provide large transfer-transport openings within the container vessel. Conventionally, therefore, the spent fuel storage pool or pit has been located externally of the reactor containment wall which peripherally surrounds the reactor and defines therewithin the reactor handling pool. Transfer tubes or conduits are disposed within the reactor containment wall and/or the fuel-handling building wall so as to fluidically connect the two pools which are located upon substantially the same elevational level. The elongated fuel assemblies are longitudinally transported in a horizontal mode through the transfer tubes or conduits between the pools as required.
In accomplishing the actual replacement of the old or spent fuel assemblies with fresh fuel assemblies, the fuel assemblies are disposed within fuel carriers or containers, and the latter are transported upon railroad-type cars movable within the transfer tubes or conduits between the two pools. Elevators and/or crane mechanisms are provided for depositing, or withdrawing, the fuel assemblies within, or from, respectively, the fuel carriers or containers in a vertical mode, and in accordance with conventional fuel-handling-transfer systems and techniques, additional means are provided for angularly moving the fuel carriers or containers to or from a horizontal disposition such that the carriers or containers may either be transported upon the railroad cars through the transfer tubes or conduits, or re-oriented in conjunction with the hoisting cranes or elevators.
In particular, one conventional fuel-handling-transfer system comprises a first hydraulic mechanism for pivotably moving, for example, the spent fuel assembly-fuel container assemblage from its vertical mode to a horizontal mode so as to be ready for translational transportation through the transfer tube or conduit upon the railroad-type car transportation system. A second mechanism, which may, for example, take the form of a reversible, electrically driven sprocket-chain drive system, translates the railroad-car vehicle, with the fuel assembly-fuel container assemblage disposed thereon, through the transfer tube and into the spent fuel storage pit or pool, and a third mechanism, which may be substantially the same as the first hydraulic mechanism, pivotably elevates the fuel assembly-fuel container assemblage to its vertical orientation. Transference of fresh fuel assembly-fuel container assemblages is understood to entail substantially the same, but reverse, processing, and this type of conventional system is exemplified by means of U.S. Pat. No. 4,053,067 issued to Leonard R. Katz et al. on Oct. 11, 1977, and assigned to the assignee of the present application, Westinghouse Electric Corporation.
It may thus be appreciated that while such conventional prior art systems obviously operate quite satisfactorily, such systems nevertheless encompass, and require, the provision of three separate, distinct, and diverse drive mechanisms. This exemplary system therefore requires separate control means which is costly to implement, and additionally renders the entire system relatively complex. Still further, processing time is necessarily extensive during the various transfer modes or steps as a result of the discontinuous pivotable and translational movements of the fuel assembly-fuel container assemblages during a transfer mode cycle as accomplished by means of the aforenoted three separate, distinct, and diverse drive mechanisms.
Another conventional fuel-handling-transfer system is disclosed within U.S. Pat. No. 3,637,096 issued to John J. Crate on Dec. 25, 1972 and assigned to Combustion Engineering, Inc. While this patented system admittedly encompasses a system wherein only a single transfer drive mechanism is employed, this conventional system is nevertheless appreciated to be costly to implement in view of the necessity of providing the extensive guide rail system for cooperating with the fuel carrier guide rollers.
Accordingly, it is an object of the present invention to provide a new and improved nuclear reactor fuel transfer system.
Another object of the present invention is to provide a new and improved nuclear reactor fuel transfer system for transferring nuclear reactor fuel assemblies between a fuel handling building and its spent fuel storage pool or pit, and the nuclear reactor containment area and its reactor handling pool.
Still another object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which overcomes the various disadvantages of the known prior art conventional systems.
Yet another object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which eliminates the requirement for multiple drive means in order to achieve the various transfer orientation modes of the fuel assembly-fuel container assemblages during a transfer process between the spent fuel storage and reactor handling pools.
Still yet another object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which is substantially more simplified than conventional nuclear reactor fuel assembly transfer systems.
Yet still another object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which accomplishes a substantial reduction in the number of drive systems required within the overall fuel assembly transfer system so as to effectively reduce the maintenance costs of the transfer system.
A further object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which effectively reduces the requisite space requirements of the overall fuel assembly transfer system by eliminating the multiple drive system characteristic of conventional fuel assembly transfer systems and replacing the same with a single drive mechanism fuel assembly transfer system.
A yet further object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which is substantially more cost-effective to implement than conventional systems in that the initial construction costs and investment required is substantially less than that of comparable conventional systems in light of the elimination of the multiple drive systems characteristic of the prior art.